Commit e8665002477f0278f84f898145b1f141ba26ee26 (PM: Allow
pm_runtime_suspend() to succeed during system suspend) removed usage
count increment across system PM.
Update doc to reflect this.
Signed-off-by: Kevin Hilman <khilman@ti.com> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>